1. Field of the Invention
The present invention relates to a method of bi-directional communication in a cellular mobile telecommunication network, wherein the downlink and uplink networks are managed separately.
2. Present State of the Art
Cellular-coverage mobile telecommunication networks have been rapidly evolving since their very appearance on the mass market in the eighties.
Initially these networks mainly supported voice services; today, however, the most pressing and significant demand concerns data services.
The ever increasing use of data applications of various kinds requires more and more bandwidth: however, this need clashes with the limits of the available radio resource.
Technologic evolution is therefore strongly stimulated by the constant demand for a performance increase as to the networks' transmission speed and capacity.
The technical solutions which may be adopted to increase the networks' capacity can be classified into two main categories:                greater frequency re-use by increasing the number of cells (which therefore become smaller and smaller in size);        definition of more efficient modulation methods, which allow for transmitting greater quantities of data on the frequency band available from time to time.        
The number of cells and modulation efficiency are however both subject to physical (and economical) limits. The limits of pico-cellular coverages are mainly given by the costs required by the numerousness of plants (apparatuses, installation, maintenance, backhauling).
It must however be observed that the smaller the cell size, and therefore the shorter the distance between the corresponding radio-base stations, i.e. between the various radio transceiving systems (“Receive Transmit Fixed Radio”, or RTFR), the more the network planning complexity increases, to such an extent that it can be assumed that the decrease in the cell size is subject to a practical limit. Said limit depends, according to case, on the propagation conditions.
On the other hand, the modulation efficiency limits depend on the fact that an extreme modulation increases the signal-to-noise ratio level (SNR) required for reception, until it becomes untenable for the transmission system.
The sophisticated transmission error correction codings employed today allow for transmission capacities close to Shannon's theoretical limit, so that they can only be used in practice for exchanging, the signal-to-noise ratio for the signals' band occupation, i.e. for optimizing the transmission speed within the band and power limits that must be complied with, which are critical especially when transmitting from a terminal to a radio base station (uplink).
Other mechanisms affecting the capacity of cellular mobile systems, such as “scheduling”, antenna systems using various diversity techniques and MIMO (Multiple Input Multiple Output), have been the subject of several studies and have already been applied within the complexity limits allowed by the current technology.
However, with the considerable growth of the demand for data transmission, it is still most important to efficiently use the frequency resources.
In addition to being a meagre resource compared to the number of users, frequencies are also lacking in relation to the number of operators; the latter, in fact, must be in a reasonable number in order to create a competitive market, with the result that the available bands are broken up and trunking efficiency is reduced.
Extensive frequency re-use by employing smaller and smaller cells or more and more directive antennas determines an increasingly sharper difference between the technical problems that must be faced in Down-Link transmission (DL) and those involved in Up-Link transmission (UL).
Downlink coverages can use bigger antenna systems to create space diversity, as well as directive beams. They have higher transmission power ratings, and can therefore serve larger coverage areas, offer higher transmission speeds, and use higher frequencies. They can use advanced low-noise receivers, and their apparatuses can be housed in conditioned environments.
Uplink coverages utilize transceivers which are subject to size, weight and emission level constraints that limit their transmission power and their use of space diversity.
High bit-rate services provided also in the uplink direction are thus placed at a disadvantage, especially in connections with relatively “far” sites. Nowadays, in fact, the uplink transmission speeds provided are usually much slower than downlink speeds.
Signalling systems are known in the art which allow network terminals for cellular-coverage mobile services to lock to a network and be assigned the radio resources (if available) that they require to be able to support the communication service requested from time to time.
Such signalling systems are based on a sequence of messages which can be represented in brief as follows:                a terminal receives a “broadcast” signal from various transceiving radio base stations:        based on different criteria (among which the quality of the received signal), the terminal locks to one of these transceiving radio base stations, called serving transceiving radio base station (or RTFR);        the terminal has all the necessary information (whether obtained from the broadcast control signal or provided by a standard) to transmit any connection requests to the serving transceiving radio base station:        vice versa, the serving transceiving radio base station has all the necessary information to notify the terminal of the arrival of any calls for it and to establish any connections;        when the terminal requests a connection, or when a call for the terminal originates from the network, the network assigns the resources for the subsequent communication steps.        
It must be pointed out that the radio base station towards which the terminal must transmit and from which it must initially receive is chosen by the terminal itself, whereas afterwards it can be “re-selected” by the terminal or by the network. At any rate, the terminal knows the serving transceiving radio base station on which it is camped.
It is also known from U.S. Pat. No. 7,177,666 a telecommunication network for mobile telephone users wherein uplink coverage is distinct from downlink coverage. In particular, uplink coverage is at least partly ensured by unidirectional radio base stations exclusively dedicated to uplink coverage, while downlink coverage is at least partly ensured by unidirectional radio base stations exclusively dedicated to downlink coverage.
However, U.S. Pat. No. 7,177,666 does not point out how to select the receiving radio base station that must serve the user terminal in the uplink section.